This invention relates generally to dispensing fuel and, more particularly, to a system and associated method for controlling vapor recovery in vacuum assist vapor recovery dispensers.
In fuel dispensing systems, such as those used for delivering gasoline to the fuel tank of a vehicle, environmental protection laws require that vapors emitted from the tank during the fuel dispensing process be recovered. Fuel is customarily delivered through a nozzle via a fuel hose and vapors are recovered from the nozzle via a vapor hose that conveys the vapor to the storage tank from whence the fuel came. In what is referred to as a balanced system, the vapors are forced through the vapor hose by the positive pressure created in the vehicle tank as the fuel enters it.
In other systems, referred to as assist-type systems, the vapor is pumped from the vehicle tank and forced into the storage tank by a vapor recovery system connected to the vapor hose. One example of an assist vapor recovery system is described in U.S. Pat. No. 6,095,204 Issued to Healy and hereby incorporated by reference. Currently, many fuel dispensing pumps at service stations are equipped with vacuum assisted vapor recovery systems that collect fuel vapor vented from the fuel tank filler pipe during the refueling operation and transfer the vapor to the fuel storage tank. Assist type vapor recovery systems use a vapor pump to “assist” in the collection of vapors generated during vehicle refueling.
One criteria of the performance of the fuel dispenser is the ratio of the vapor or air being recovered and returned to the underground storage tank (UST) to the fuel or liquid being pumped from the UST to the vehicle. However, certain variables may affect the valve of the air-to-liquid (A/L) ratio and these variables need to be accounted for to provide a consistent and reliable refueling operation. Typical variables include the pressure drop of the hose and nozzle, the speed of the pump with varying flow rates, meter outputs from grade to grade, pump wear, etc.
Fuel dispensing systems at service stations having vacuum assisted vapor recovery capability which are unable to account for these and other variables waste energy, increase wear and tear, ingest excessive air into the underground storage tank and cause excessive pressure buildup in the piping and UST due to the expanded volume of hydrocarbon saturated air. Such problems could become systematic and present a significant issue that must be addressed.